code: def input_spec(self):
      spec = super().input_spec()
      spec["sentence"] = types.TextSegment(required=False, default="")
      return spec
  
imports: from collections.abc import Iterable, Iterator
  from absl.testing import absltest
  from lit_nlp.api import types
  from lit_nlp.components import ablation_flip
  from lit_nlp.examples.models import glue_models
  import numpy
  from lit_nlp.lib import file_cache
label_desc: Use image node_id 1 for calling the SST2ModelNonRequiredField obj's underlying member method code with example usage: obj.input_spec() and returns: spec